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We discuss the cyclic homology of crossed product algebras from the Cuntz-Quillen point of view. The periodic cyclic homology of a crossed product algebra $A\rtimes G$ is described in terms of the $G$-action on periodic cyclic bicomplexes…

K-Theory and Homology · Mathematics 2022-10-19 Michael Puschnigg

Using the Baum-Connes conjecture with coefficients, we develop a K-theory formula for reduced C*-algebras of strongly $0$-$E$-unitary inverse semigroups, or equivalently, for certain reduced partial crossed products. In the case of…

Operator Algebras · Mathematics 2021-09-15 Xin Li

We give a general formula for the equivariant complex $K$-theory $K_G^*(V)$ of a finite dimensional real linear space $V$ equipped with a linear action of a compact group $G$ in terms of the representation theory of a certain double cover…

K-Theory and Homology · Mathematics 2009-03-06 Siegfried Echterhoff , Oliver Pfante

Let $\Omega$ be a tiling space and let $G$ be the maximal group of rotations which fixes $\Omega$. Then the cohomology of $\Omega$ and $\Omega/G$ are both invariants which give useful geometric information about the tilings in $\Omega$. The…

Operator Algebras · Mathematics 2015-06-17 Charles Starling

Let $C^*(E)$ be the graph $C^*$-algebra associated to a graph E and let J be a gauge invariant ideal in $C^*(E)$. We compute the cyclic six-term exact sequence in $K$-theory of the associated extension in terms of the adjacency matrix…

Operator Algebras · Mathematics 2012-11-20 Toke M. Carlsen , Søren Eilers , Mark Tomforde

Let a compact group G act on real or complex C*-algebras A and B, with A separable and B sigma-unital. We express the G-equivariant Kasparov groups KK_n(A,B) by algebraic K-groups of a certain additive category.

K-Theory and Homology · Mathematics 2007-05-23 Tamaz Kandelaki

We introduce a version of algebraic $K$-theory for coefficient systems of rings which is valued in genuine $G$-spectra for a finite group $G$. We use this construction to build a genuine $G$-spectrum $K_G(\mathbb{Z}[\underline{\pi_1(X)}])$…

Algebraic Topology · Mathematics 2026-02-02 Maxine Calle , David Chan , Andres Mejia

An action of Z^l by automorphisms of a k-graph induces an action of Z^l by automorphisms of the corresponding k-graph C*-algebra. We show how to construct a (k+l)-graph whose C*-algebra coincides with the crossed product of the original…

Operator Algebras · Mathematics 2007-06-26 Cynthia Farthing , David Pask , Aidan Sims

For a compact simply connected simple Lie group $G$ with an involution $\alpha$, we compute the $G\rtimes \Z/2$-equivariant K-theory of $G$ where $G$ acts by conjugation and $\Z/2$ acts either by $\alpha$ or by $g\mapsto \alpha(g)^{-1}$. We…

K-Theory and Homology · Mathematics 2014-01-31 Po Hu , Igor Kriz , Petr Somberg

We develop general methods to compute the algebraic $K$-theory of crossed products by Bernoulli shifts on additive categories. From this we obtain a $K$-theory formula for regular group rings associated to wreath products of finite groups…

K-Theory and Homology · Mathematics 2026-01-21 Julian Kranz , Shintaro Nishikawa

We compute the $RO(A)$-graded coefficients of $A$-equivariant complex and real topological $K$-theory for $A$ a finite elementary abelian $2$-group, together with all products, transfers, restrictions, power operations, and Adams…

Algebraic Topology · Mathematics 2022-10-12 William Balderrama

We compute the topological K-theory of the group C*-algebra C*_r(G) for a group extension Z^n->G->Z/m provided that the conjugation action of Z/m on Z^n is free outside the origin.

Algebraic Topology · Mathematics 2011-09-08 Martin Langer , Wolfgang Lueck

There are many classes of nonsimple graph C*-algebras that are classified by the six-term exact sequence in K-theory. In this paper we consider the range of this invariant and determine which cyclic six-term exact sequences can be obtained…

Operator Algebras · Mathematics 2015-10-30 Søren Eilers , Takeshi Katsura , Mark Tomforde , James West

Let P be a semigroup that admits an embedding into a group G. Assume that the embedding satisfies a certain Toeplitz condition and that the Baum-Connes conjecture holds for G. We prove a formula describing the K- theory of the reduced…

Operator Algebras · Mathematics 2012-05-25 Joachim Cuntz , Siegfried Echterhoff , Xin Li

Let $p$ be a prime. We calculate the connective unitary K-theory of the smash product of two copies of the classifying space for the cyclic group of order $p$, using a K\"{u}nneth formula short exact sequence. As a corollary, using the Bott…

Algebraic Topology · Mathematics 2010-08-03 Robert Bruner , Khairia Mira , Laura Stanley , Victor Snaith

Let $\Uq$ be a quantum group. Regarding a (noncommutative) space with $\Uq$-symmetry as a $\Uq$-module algebra $A$, we may think of equivariant vector bundles on $A$ as projective $A$-modules with compatible $\Uq$-action. We construct an…

Quantum Algebra · Mathematics 2009-12-21 G. I. Lehrer , R. B. Zhang

We derive the Pimsner-Voiculescu sequence calculating the K-theory of a $C^{*}$- algebra with $\mathbb{Z}$-action using constructions with equivariant coarse K-homology theory. We then investigate to which extend this idea extends to more…

Operator Algebras · Mathematics 2021-12-21 Ulrich Bunke

We consider the algebraic K-theory of a truncated polynomial algebra in several commuting variables, K(k[x_1, ..., x_n]/(x_1^a_1, ..., x_n^a_n)). This naturally leads to a new generalization of the big Witt vectors. If k is a perfect field…

Algebraic Topology · Mathematics 2013-10-08 Vigleik Angeltveit , Teena Gerhardt , Michael A. Hill , Ayelet Lindenstrauss

In this paper, we develop a quantitative K-theory for filtered C*-algebras. Particularly interesting examples of filtered C*-algebras include group C*-algebras, crossed product C*-algebras and Roe algebras. We prove a quantitative version…

Operator Algebras · Mathematics 2012-04-17 Hervé Oyono-Oyono , Guoliang Yu

For $A$ a $C^*$-algebra, $E_1, E_2$ two Hilbert bimodules over $A$, and a fixed isomorphism $\chi : E_1\otimes_AE_2\to E_2\otimes_AE_1$, we consider the problem of computing the $K$-theory of the Cuntz-Pimsner algebra ${\mathcal…

Operator Algebras · Mathematics 2007-07-13 Valentin Deaconu